IL-6 is a cytokine which is also called B cell stimulating factor 2 (BSF2) or interferon β2. IL-6 was discovered as a differentiation factor involved in the activation of B-lymphocytic cells (Hirano, T. et al., Nature (1986) 324, 73-76). Thereafter, it was found to be a multifunctional cytokine that influences various functions of cells (Akira, S. et al., Adv. in Immunology (1993) 54, 1-78). IL-6 has been reported to induce the maturation of T-lymphocytic cells (Lotz, M. et al., J. Exp. Med. (1988) 167, 1253-1258).
IL-6 transmits its biological signal through two proteins on the cell. One of them is IL-6 receptor, a IL-6-binding protein with a molecular weight of about 80 kD, (Taga, T. et al., J. Exp. Med. (1987) 166, 967-981; Yamasaki, K. et al., Science (1987) 241, 825-828). IL-6 receptor exists not only in the membrane-bound form with transmembrane domain expressed on the cell surface but also as a soluble IL-6 receptor consisting mainly of the extracellular region.
The other is a membrane-bound protein gp130 having a molecular weight of about 130 kD that is involved in non-ligand-binding signal transduction. IL-6 and IL-6 receptor form the IL-6/IL-6 receptor complex, which after binding to gp130 transmits its biological signal to the cell (Taga, T. et al., Cell (1989) 58, 573-581).
IL-6 antagonists are substances that inhibit the transduction of biological activity of IL-6. As the IL-6 antagonists, there have been known so far antibody against IL-6 (anti-IL-6 antibody), antibody against IL-6 receptor (anti-IL-6 receptor antibody), and antibody against gp130 (anti-gp130 antibody), altered IL-6, partial peptides of IL-6 or IL-6 receptor and the like.
Anti-IL-6 receptor antibody has been described in several reports (Novick D. et al., Hybridoma (1991) 10, 137-146, Huang, Y. W. et al., Hybridoma (1993) 12, 621-630, International Patent Publication WO 95/09873, French Patent Application FR 2694767, U.S. Pat. No. 521,628). Humanized PM-1 antibody has been known that was obtained by grafting the complementarity determining region (CDR) of a mouse antibody PM-1 (Hirata, Y. et al., J. Immunology (1989) 143, 2900-2906) to a human template antibody (the International Patent Publication WO 92-19759).
Inflammatory bowel disease (IBD) is a nonspecific inflammation represented by ulcerative colitis and Crohn's disease. Immunological disturbances have been implicated in the onset of the disease, but that has not led to the elucidation of the etiology. It is believed, however, that monocytes and lymphocytes that clustered at lesion sites are involved in the damages of mucus, and inflammatory mediators, in particular cytokines (such as IL1β, TNFα, and IL-6) are drawing special attention.
For IL-6 among the inflammatory mediators, attention has been given to its relation to the disease status or to whether it could be an specific index for IBD. Serum level of IL-6 increases in both of Crohn's disease and ulcerative colitis, and the level correlates with the condition of the disease (Holtkamp, W. et al., J. Clin. Gastroenterology (1995) 20, 123-126, Niederau, C. et al., Hepato-Gastroenterology (1997) 44, 90-107). Measurement of amount of IL-6 mRNA in the tissue as PCR (polymerase chain reaction) products has revealed that it well correlated to the disease status of both ulcerative colitis and Crohn's disease (Stevens, C. et al., Dig. Dis. Sci. (1992) 37, 818-826). On the increase of IL-6 production during active IBD, the mechanism was analyzed and it was found that the amount of production when mononuclear cells in the lamina propria are stimulated by Pokeweed mitogen, are well correlated with the condition of disease (Reinecker, H. -C. et al., Clin. Exp. Immunol. (1993) 94, 174-181).
Thereafter, the correlation of IL-6 production and disease status was observed in the culture of mononuclear cells derived from the lamina propria and the tissue culture of the mucosa from patients. In the former case, it was also shown that the number of cells that produce IL-6 in the mucosal tissue also increased. Among the mononuclear cells the most important IL-6-producing cells are macrophage, and it has been confirmed that there are a great number of CD68-positive macrophages that vigorously produce IL-6 in the lamina propria of the IBD patients in the active stage (Kusugami, K. et al., Dig. Dis. Sci. (1995), 40, 949-959).
It has also been found that the production of IL-6 correlates to the endoscopic observation of patients with Crohn's disease (Reimund, J. -M. et al., Gut (1996) 39, 684-689). In addition, there are some reports that not only IL-6 but soluble IL-6 receptor concentration in serum well correlates with the disease status (Mitsuyama, K. et al., Gut (1995) 36, 45-49).
For inflammatory mediators other than IL-6, the amount of IL-1β production is also known to correlate to condition of disease. On the other hand, this is not always true for TNF-α and the amount of production may tend to be high in low activity in disease condition (Reinecker, H. -C. et al., Clin. Exp. Immunol. (1993) 94, 174-181, Reimund, J. -M. et al., Gut (1996) 39, 684-689).
The current method of treating IBD comprises a combination of diet and medication, with salazosulfapyridine, glucocorticoid, etc. being prescribed. For these drugs, however, there are intolerant patients due to their side effects, and thereby problems occur in terms of a long-term administration.
On the other hand, some trials are going on as a new treatment of IBD that intends to improve disease conditions through the inhibition of cytokine activity. Its main targets are IL-1 and TNF-α (Van Deventer, S. J. H. Gut (1997) 40, 443-448); for IL-1, an IL-1 receptor antagonist (Cominelli F. et al., Gastroenterology (1992) 103, 65-71) and an IL-1 inhibitor, CGP47969A (Casini-Raggi et al., Gastroenterology (1995) 109, 812-818), and the like are under study on the clinical or the experimental animal level. For TNF-α, specific monoclonal antibody has been administered to patients with Crohn's disease, in which reduced activity and cured ulcer have been observed (Van Dullemen, H. M. et al., Gastroenterology (1995) 109, 129-135). It was not known, however, that IL-6 antagonist can treat IBD to specifically suppress the biological activity of IL-6.